The present invention relates generally to fastener driving tools such as combustion powered tools, pneumatic tools, cordless framing tools and the like. More particularly, the present invention relates to improvements in a device which adjusts the depth of drive of the tool.
Such tools typically have a housing enclosing a power source, such as combustion, pneumatic, electric or powder, a trigger mechanism and a magazine storing a supply of fasteners for sequential driving. The power source includes a reciprocating driver blade which separates a forwardmost fastener from the magazine and drives it through a nosepiece into the workpiece. The nosepiece is also the conventional attachment point for the magazine and defines the entryway for fasteners from the magazine into a fastener passage where impact with the driver blade occurs, as well as subsequent transport into the workpiece.
One operational characteristic required in many types of fastener driving applications is the ability to predictably control fastener driving depth. For the sake of appearance, some trim applications require fasteners to be countersunk below the surface of the workpiece, others require the fasteners to be sunk flush with the surface of the workpiece, and some may require the fastener to stand off above the surface of the workpiece. Depth adjustment has been achieved in pneumatically powered and combustion powered tools through a tool controlling mechanism, referred to as a drive probe that is movable in relation to the nosepiece of the tool. The range of movement of the depth adjustment defines a range for fastener depth-of-drive. Similar depth of drive adjustment mechanisms are known for use in combustion type framing tools.
Besides trim applications, there are other instances where fastener driving depth is important, including but not limited to siding and wallboard installation. It has been found that fastener depth of drive varies significantly based on the tool power source as well as the characteristics of the workpiece or substrate. Improperly adjusted fastener driving tools leave fasteners incompletely driven into the workpiece, or cause dents or dimples to the workpiece through overdriving.
U.S. Pat. No. 5,320,268, incorporated by reference, discloses a powered fastener driving tool designed for creating a dimple in wallboard during the fastener driving process. A relatively large shoe-type workpiece contact element (WCE) includes a reciprocating dimpler which is engaged by the driver blade to create a dimple as the fastener is being driven. In this unit, the dimpler is a separate component and is spring biased relative to the nosepiece as well as to the WCE. This construction is relatively complex, and is not always required for tool applications where flush driving of fasteners is desired, as in the installation of siding or other applications. In such applications, the creation of dimples in the workpiece is considered counterproductive and is to be avoided.
In U.S. Pat. No. 6,695,192, incorporated by reference, a fastener driver is disclosed wherein the WCE is connected to and movable with the internal bumper that engages the reciprocating piston. In this tool, impact on the workpiece is regulated by the independent WCE movement relative to the nosepiece. This system is effective in absorbing shock generated in fastener driving to reduce unwanted “second strike” or workpiece damage caused by tool recoil, as well as user difficulty in accurately maintaining the tool in position during fastener driving. However, the configuration of the WCE in this unit is considered relatively complicated. Also, it has been found that a drawback of providing relatively large WCE's is that in some applications they obscure the workpiece, thus interfering with accuracy in fastener driving.
Thus, there is a need for an improved depth of drive mechanism for a fastener driving tool in which combustion cycle impact forces on the workpiece are reduced. There is also a need for such an improved depth of drive mechanism which is less complicated than prior art designs. In addition, there is a need for an improved depth of drive mechanism for a fastener driving tool which facilitates user visibility of the workpiece.